Monitoring circuit



May 15, 1934. F. A. cowAN 1,958,510

MONITORING CIRCUIT Filed Oct. 6. 1931 VVVVVVV AAAIA lhAH u AAAAAAAA T L ;Mm'tgrmg Set E. Z2 .25 LLl onglet ng INVENTOR EH Cba/zzn ATTORN EY Patented May 15, 1934 UNITED STATES PATENT OFFICE MONITORING CIRCUIT Application October 6, 1931, Serial No. 567,273

5 Claims.

This invention relates to transmission circuits, and more particularly, to arrangements for mon.- itorng the same.

In monitoring a one-way transmission circuit such as a program circuit which is divided into sections each of which is terminated in a oneway ampliiier, it is desirable to connect the monitoring set for a given line section to the output side of the repeater in order that the monitoring set may detect noise originating in any part of the repeater, as well as in any part of the transmission line section. It is also desirable that the monitoring set should be so associated with the circuit that when a tone or other signal is applied to the lineY section which is being tested, noise from the succeeding line section will not be picked up by the monitoring set.

These objects are accomplished in accordance with the present invention by associating the monitoring set with the output side of the repeater of agiven line section through a balanced circuit arrangement such that the monitoring set is substantially conjugate with respect to the succeeding line section. Preferably, the balancing arrangement includes a hybrid coil connected in the output circuit of the repeater, the monitoring set being connected to one terminal of the secondary of the hybrid coil, and the outgoing or succeeding line section being connected to the other terminal of the secondary of the hybrid coil, so that the outgoing line will be conjugate with respect to the monitoring set, but, both the outgoing line and the monitoring set may receive transmission from the repeater.

The invention will now be more fully understood from the following description when read in connection with the accompanying drawing, Figure 1 of which shows a repeater arrangement between two line sections with a monitoring connection associated therewith, and Fig. 2 of which shows the hybrid coil connection for the monitoring set of Fig. l in a simplied and conventional form in order to render` its operation more clear.

Referring to Fig. 1, two line sections L1 and L2 are shown interconnected through a two-stage repeater of the push-pull type. The iirst stage of the repeater includes amplifying tubes V1 and V1 connected in push-pull relation, and the second stage of the repeater includes vacuum tubes V2 and V2 connected in push-pull relation. The line section L1 is connected to the push-pull amplifier through a transformer T, and a potentiometer P is provided on the input side of the transformer T in order to control the gain of the one-way amplifier. The plate current is supplied to the tubes V1 and V1 from the battery B through the choke coil M1 which is connected to the junction point of resistances R1 and R1 associated with the plate circuits of the tubes V1 and V1, respectively, The filaments of the tubes V1 and V1 are connected to the junction point of the resistances R1 and R1 for alternating current transmission through a capacity K1. In a similar manner the plate potential is supplied to the tubes V2 and V2 through the choke coil M2 which is connected to the junction point of the primary windings of the hybrid coil H, said junction point being connected to the -iilaments of the tubes V2 and V2 for alternating current transmission through the capacity K2.

The filament current for the tubes is supplied by the battery A with respect to which the lilaments of the four tubes are connected in series. The C or grid potential for tube V1 is obtained by connecting the grid of said tube to the junction point of the resistances r1 and r2 which are connected across the iilament of the tube V1, and the grid potential for the tube V1 is obtained by connecting the grid of said tube to the remaining terminal of the resistance r1. By connecting the two grids to the opposite terminals of the resistance r1, the drop through said resistance compensates for the difference in the filament potentials of the two tubes due to the fact that they are in series.

In order that proper grid potentials may be applied to the tubes V2 and V2 resistances R2 and R2 are connected from the grids of said tubes to a common point from which a connection 10 extends to a resistance T5 in the filament supply circuit 11. If desired, the grid potential thus derived from the battery A may be augmented by supplying a supplementary battery C in the connection l0. Owing to the difference in the nlament potentials of the tubes V2 and V2 due to the fact that they are connected in series, it is necessary that the potential applied to the grid of the tube V2 should be more negative than that applied to the grid of the tube V2 in order that the grid iilament drops of the two tubes may be the same. This result is accomplished by including a small supplemental battery C1 in circuit with the resistance R2, this battery having such potential as t0 just compensate for the drop through the lilament of the tube V2 and its associated resistance r4.

By means of the circuit arrangement above described, a two-stage push-pull amplifier is obtained. This ampliiier has the same potential drops for both tubes oi' the same stage, notwithstanding the fact that the laments of the tubes are connected in series. The circuit is also arranged in such manner that the second stage tubes may be biased to a different potential from the iirst stage tubes.

The hybrid coil I-I associated with the output oi the repeater includes primary coils l and 2 and secondary coils 3, 4, 5 and 6. The resistance X has one terminal connected to the junction points of the coils 3 and 4, and its other terminal connected to the junction points of the coils 5 and 6. The remaining terminals of the coils 3 and 6 are connected to the output line L2, and the monitoring set is connected to the remaining terminals of the coils 4 and 5, as shown.

The operation of this hybrid coil connection will be more easily understood from the diagram of Fig. 2 in which the hybrid coil and associated circuits are redrawn in a more common and conventional form. Here it will be seen that the output of the amplifier and the resistance X connected to the junction points of the secondary windings or" the hybrid coil are conjugate so that no energy is transmitted from the output of the repeater to the resistance X, It will also be noted that the output line L2 and the monitoring set are connected to the points where, in the conventional hybrid coil arrangement of the 22 repeater, the line and balancing network, respectively, are connected. Consequently, the outgoing line L2 and the monitoring set will be conjugate so that neither can transmit nor receive from the other.

Since it is more important that the hybrid coil eiciently transmit energy from the repeater to the line section L2 than it is that it should transmit to the monitoring set, the hybrid coil is made unsymmetrical by making the windings 3 and 6 relatively larger than the windings 4 and 5, This may be done without disturbing the requisite conditions of conjugacy if the impedances of the line L2, the monitoring set, the resistance X, and

the output of the repeater, are properly propor- Y tioned. By having the hybrid coil circuit thus unsyrnmetrically arranged thel greater part of the energy transmitted through the repeater will be passed on to the output line L2, and a relatively small part of the energy will be diverted into the monitoring set if the monitoring set should be inadvertently left connected in circuit while a program is being transmitted. It will be understood, of course, that should the monitoring set be open`circuited, no eiect will be produced upon the line because the monitoring set and the line are conjugate.

By having the monitoring set connected to the secondary side of the hybrid coil, the monitoring set is enabled to detect noise originating in any part of the repeater, as well as in the transmission line L1. If the monitoring set were connected at some intermediate point in the repeater, or ahead of the repeater, the absence of noise in the monitoring set would not necessarily indicate that no noise was present in any part of the circuit, as noise in the repeater or in that part of the repeater beyond the monitoring set would not affect the monitoring set, and yet, would be transmitted over the outgoing line L2.

By connecting the monitoring set through the hybrid coil arrangement above described, the monitoring operator in listening for noise on the line section L1 and the associated repeater, will know that if any noise is heard it can only come from some point in the line L1 or the repeater connected thereto, as noise from the line L2 cannot be transmitted to the monitoring set through the hybrid coil, due to the conjugacy existing between the line L2 and the monitoring set. Noise or energy incoming from the line L2 divides between the resistance X and the plate circuits of the ampliiier without being transmitted through the coils 4 and 5 to the monitoring set. A similar condition of conjugacy exists for transmission in the opposite direction so that if the monitoring operator should inadvertently leave a tone connected to the hybrid coil through the monitoring set, this tone would divide between the resistance X and the plate circuits of the repeater without passing on to the line L2. The tone cannot, of course, be transmitted to the line L1 due to the one-way characteristic of the Vacuum tubes of the repeater.

Due to the features above pointed out, a program can be transmitted over the line L1 and through the repeater to the line L2 without being interfered with by the connection of the monitoring set to the circuit, and the operator may ,n

monitor on the circuit either while the program is being transmitted or during timesthat the circuit is not being used except for testing purposes. Y I

It will be obvious that the general principles herein disclosed may be embodied in many other organizations widely different from those illustrated, without departing from the spirit of the invention as deiined in the following claims.

What is claimed is:

l. In a transmission circuit, an incoming line section, an outgoing line section, an amplifier interposed between said line sections, a balanced circuit connection between the output of said amplifier and said outgoing line section, a monitoring circuit connected to points of said balanced circuit which are neutral with respect to said outgoing line but which are non-conjugate with respect to said amplifier, and the parts of said balanced connection being so unsymmetrically related to said points that more energy will be transmitted from the amplier to the outgoing line circuit than to said monitoring circuit.

2. In a transmission circuit, an incoming line section, an outgoing line section, an amplier Vinterposed between said line sections, a hybrid coil having two of its four sets of terminals connecting the output of said ampliiier to said outgoing line, a balancing impedance connected to a third set of terminals, and a monitoring circuit connected to a set of terminals of said hybrid coil which are conjugate with respect to said outgoing line and non-conjugate with respect to said ampliiier. Y

3. In a transmission circuit, an incoming line section, an outgoing line section,'an amplier interposed between said line sections, a hybrid coil connecting the output of said amplifier to said outgoing line, and a monitoring circuit, said repeater being connected to the input winding of said hybrid coil, and said monitoring circuit and outgoing line being connected respectively to opposite terminals of the secondary windings of said hybrid coil.

4'. In a transmission circuit, an incoming line section, an outgoing line section, an amplifier interposed between said line sections, a hybrid coil connecting the output of said amplifier to said outgoing line, a monitoring circuit, and a balancing circuit, said repeater being connected to the input winding of said hybrid coil, said network being connected to the neutral points of to the input winding of said hybrid coil, said network being connected to the neutral points of the secondary windings of said hybrid coil, and the monitoring circuit and outgoing line being connected to the opposite end terminals of said hybrid coil, said secondary coils being so unsymmetrically wound that more energy is transmitted from the repeater to the outgoing line than is transmitted to the monitoring circuit.

. FRANK A. COWAN. 

